1. Field of the Invention
The present invention relates to an internal combustion engine control apparatus.
2. Description of the Related Art
Japanese Patent Application Laid-Open (JP-A) No. H11-210608 discloses an internal combustion engine control apparatus which activates a catalytic converter to maintain desired purification performance soon after an internal combustion engine starts. According to the control apparatus, controllability and stability of the rotational speed of the internal combustion engine are improved by an intake air mass more than that at a normal idle state and feedback control of an ignition timing so as to maintain a desired engine speed during a period after the engine starts. Specifically, the control apparatus includes an air intake mass control unit and an ignition timing control unit. The air intake mass control unit increases the air intake mass at an idle state where exhaust gas is discharged through the catalytic converter after the engine starts, by a predetermined mass from an air intake mass at the normal idle. The ignition timing control unit retards the ignition timing by controlling the ignition timing based on a command value which is generated by a feedback control in which the rotational speed of the internal combustion engine is maintained at the desired speed after the air intake mass control unit starts increasing the air intake mass. The air intake mass control unit also includes a unit that decreases the increase in the air intake mass when the command value generated by the feedback control indicates a spark angle retarded from a retard threshold, which is set within a predetermined allowable range of the ignition timing capable of normally operating the internal combustion engine.
In the internal combustion engine control apparatus of JP-A No. H11-210608, when the command value of the ignition timing is advanced from the threshold described above, a correction mass by which the increase in the air intake mass is decreased is set as a current correction mass. Further, the air intake mass control unit sets the increase, which is not corrected, of the air intake mass in accordance with a temperature of the internal combustion engine. Further, the air intake mass control unit gradually increases the increase, which is not corrected, of the air intake mass right after the engine starts. The air intake mass control unit also gradually decreases the increase, which is not corrected, of the air intake mass in a predetermined way with time after a predetermined time is passed from the start of the control for increasing the air intake mass.
It is desired that the correction mass (controlled variable) of the air intake mass after the internal combustion engine starts is set to a more appropriate value. There are described here two cases where the correction mass is set to an inappropriate value.
One case is as follows. In the internal combustion engine control apparatus of JP-A No. H11-210608, the air intake mass control unit gradually decreases the increase, which is not corrected, of the air intake mass in the predetermined way with time after the predetermined time is passed from the start of the control for increasing the air intake mass. However, excess and deficiency in the air mass might be caused at a middle temperature of the internal combustion engine while warming up the internal combustion engine. An error in the air intake mass is caused by the air intake mass decreased due to a property of an idle speed control valve (ISCV) or a property of a throttle valve (change in properties with time), mainly depending on the opening angle of the valve. Hence, decreasing the increase in the air mass with time causes an inconsistency.
The other case is as follows. In the internal combustion engine control apparatus of JP-A No. H11-210608, the air intake mass is increased and decreased based on the command value of the ignition timing generated by an ignition feedback (F/B) control. However, the command value of the ignition timing also depends on a fuel property, an engine friction, and the like. For example, when a heavy fuel is used, an air/fuel ratio is lean, so that an output torque is decreased and an engine speed is decreased. Consequently, the ignition timing is advanced by the ignition feedback control. In the internal combustion engine control apparatus, an excessive air mass might be obtained since the air mass might be increased when the ignition timing is advanced. The engine speed differs from a desired speed not only because of the excess and the deficiency of the air intake mass, but because of the fuel property, the engine friction, and the like. Hence, the air intake mass might be excessively corrected when the air intake mass is increased and decreased based on the command value of the ignition timing. Therefore, it is considered to obtain the correction mass of the air intake mass based on a deficient mass. Here, the excess and the deficiency of an actual air mass with respect to the desired air mass is detected by directly measuring an actual air intake mass, and the deficient mass is obtained when the actual air mass is deficient with respect to the desired air mass. However, in the process described above, the ignition timing might not be stabilized at the desired value when a measuring instrument for directly measuring the actual air intake mass has an error (including manufacturing error) since the air intake mass is excessively corrected.
An object of the present invention is to provide an internal combustion engine control apparatus in which a correction mass of an air intake mass after an internal combustion engine starts is set to a more appropriate value.